The present invention relates to a fuel injection control apparatus, and more specifically to a fuel injection control apparatus responsive to an output signal from an electromagnetic induction type engine speed sensor.
An electromagnetic induction type engine speed sensor is employed for electronic fuel injection systems to maximize engine operating efficiency. The amount of fuel to be supplied to engine cylinders is calculated in accordance with engine operating parameters including the engine speed parameter detected by the wheel speed sensor. More specifically, in a gasoline powered engine, the fuel injection valve is opened in response to the rotational speed signal at a predetermined crankshaft angle and is closed after a prescribed amount of time following the opening of the valve. In a Diesel engine, on the other hand, a solenoid valve is closed in response to a rotational speed signal generated at a predetermined angular position of the crankshaft to inject fuel through a delivery valve or the like and through a nozzle into the engine, and the valve is opened in response to the speed signal to terminate the fuel injection in a manner similar to that shown and described in Japanese Provisional Specification 58-187537.
Since the voltage output of the wheel speed sensor is a sinusoidal wave (as indicated by a solid line in FIG. 6) the frequency and amplitude of the voltage drops as engine speed decreases (as indicated by the broken line). If an engine starter is operated with low battery voltage or at low ambient temperatures, the engine starter would fail to supply enough power to the engine for startup, and the sensor voltage would not represent a valid speed indication. If the sensor voltage is utilized as an engine operating parameter under such conditions, fuel injection calculation would result in a failure to properly start the engine.